1. Field of the Invention
The present invention relates to a display device in which display panels, such as passive matrix liquid crystal panels, active matrix liquid crystal panels, or organic EL panels used in an electronic notepad or in portable equipment such as a cellular telephone, are provided on both sides of the display device. More specifically, the present invention relates to an IC wiring structure for driving panels on both sides of the display device.
2. Description of the Related Art
In the conventional display devices, for example, STN liquid crystal display devices, a dot matrix is configured by disposing segment electrodes and common electrodes in a matrix shape. An orienting film of a material such as polyimide is formed on a surface of each electrode, and a liquid crystal layer is provided between the electrode surface and the orienting film. A screen is driven by applying voltage to each of the electrodes in a time division manner. An output electrode of a driver IC is connected to each segment electrode and to each common electrode, and the driver IC driver applies signals to each of the electrodes. Segment signals and common signals applied to each of the electrodes differ. The driver IC that outputs the segment signals and the common signals is configured by one chip when the number of pixels is on the order of 160×128 dots. On the other hand, specific drivers are used respectively as the driver ICs for the segment signals and the common signals when the number of pixels is, equal to or higher than 160×128 dots. The driver IC may be also used in plural, depending upon a relationship between the number of driver signals output by the driver ICs and the number of pixels. Shell type structures that open into two parts have been widely employed in cellular telephones in recent years. Cellular telephones having increased their market shares have such a form that a main screen and a rear surface sub-screen are installed as display screens so that the two screens are displayed on both sides (hereinafter called a double-sided panel). The two screens include separate display panels (refer to JP 2000-338483 A, for example). ICs for driving the display panels are mounted to each of the display panels to thereby drive both screens. Alternatively, one driver IC that corresponds to the combined number of pixels of both display screens is used to drive both screens. In the latter case, when STN liquid crystals are used, for example, the segment signals are extracted from a side that is opposite to a side connected to the main display panel. The segment signals are then input to the sub-display panel by a film substrate and commonly used. Further, the common electrodes for the main display are disposed on both sides of connection terminals for the segment signals. Further, common electrodes for the sub-display are disposed on both sides of the common electrodes for the main display. The common signals used only for the sub-display are input to the common electrodes for the sub-display on the main display panel. The signals used only for the sub-display are input to the sub-display panel via an outer circumferential of the main display panel, similarly to the segment signals, to thereby drive both screens.
Alternatively, with a method of branching off the signals output from the ICs at terminals connected to the main panel and supplying the signals to the sub-panel by using a flexible substrate, for example, the common signals can also be commonly used, in addition to the segment signals.
Problems like those described below, however, exist with the conventional panels.
(1) The number of pixels differs between the main panel and the sub-panel, so that only a portion of the main panel can be displayed in the double-sided sub-panel.
(2) In a case where the main panel is a color display and the sub-panel is a monochrome display, when the segment signals of the main panel are supplied to the sub-panel as is, it is difficult to handle data for displaying characters and pictures because R, G, and B segment signals correspond to one pixel in the main panel.